Melt-Formed Inorganic Fibres

ABSTRACT

A needled blanket is provided comprising melt-formed inorganic fibres having an overall composition in weight percent SiO2: 47 to 65%; AI2O3: 35 to 53%; the blanket having • a shot content, of shot &gt;45 μm, of less than 51 wt %, • a specific surface area [BET)&gt;0.25 m2·g−1. also disclosed are fibres for producing such blankets, and self-supporting products made from such fibres.

FIELD OF THE INVENTION

This invention relates to aluminosilicate fibres, blankets made from such fibres, and other products made from such fibres.

BACKGROUND Inorganic Fibres

Inorganic fibrous materials are well known for their use as thermal and/or acoustic insulating materials and are also known for their use as strengthening constituents in composite materials such as, for example, fibre reinforced cements, fibre reinforced plastics, and as a component of metal matrix composites. Such fibres may be used in support structures for catalyst bodies in pollution control devices such as automotive exhaust system catalytic converters and diesel particulate filters and may be used in the catalyst bodies themselves. Such fibres may be used as a constituent of friction materials [e.g. for automotive brakes].

Inorganic fibres for use in insulation are well known. A convenient means of providing insulation from inorganic fibres is as blankets comprising said fibres. Since these blankets are to be used as thermal insulation, it is imperative that their thermal conductivity be as low as possible.

In addition, in many applications it is preferable for the blanket to have a low density. For example, in vehicles the lower the density (and thus mass) of thermal insulation carried, the less of a burden the thermal insulation is, and so the vehicle's performance, is correspondingly increased.

There is therefore always a need to produce inorganic fibres which, when made into blankets, attain lower thermal conductivities at a given density than previously achieved.

Thermal Conductivity of Bodies Of Inorganic Fibres

Thermal conductivity of a body of melt formed fibres (e.g. a blanket or other product form) is determined by a number of factors including in particular:

-   -   Diameter of the fibres; and     -   “Shot” (unfiberised material) content

Fine diameter fibres provide low thermal conductivity to a body of fibres by reducing the scope for conduction through the solid and permitting finer inter-fibre porosity increasing the number of radiate-absorb steps for heat to pass by radiation from one side of the body to the other.

The presence of shot in a blanket increases thermal conductivity of the blanket by increasing the scope for conduction through the solid. Shot also increases the density of a blanket. The lower the shot content, the lower the thermal conductivity and density. For two bodies of identical fibre content and chemistry, the body with the lower shot content will have both the lower density and lower thermal conductivity. Additionally, more shot means less fibres and therefore implies less material to aid in reducing thermal conductivity.

Manufacturing Processes for Inorganic Fibres

Inorganic fibres can be made by a variety of routes. Prior to 1987 there were four principle types of fibrous materials used for making thermal insulation products [such as, for example, blanket, vacuum formed shapes, and mastics]. These were made by two principal manufacturing routes, although the details of the particular routes vary according to manufacturer. The fibres and routes were (in order of increasing cost and temperature performance):

Melt Formed Fibres

-   -   Glass wools     -   Mineral wools     -   Aluminosilicate fibres

Sol-Gel Process Fibres

-   -   So-called polycrystalline fibres

Sol-gel process fibres tend to be more expensive than melt formed fibres as they are significantly more complex to make. The present disclosure does not relate to sol-gel process fibres but to melt formed fibres.

Because of the history of asbestos fibres, a lot of attention has been paid to the relative potency of a wide range of fibre types as a cause of lung disease. Studies of the toxicology of natural and man-made fibres led to the idea that it was the persistence of fibres in the lung that caused problems. Accordingly, the view developed that if fibres can be removed from the lung quickly, then any risk to health would be minimised.

The concepts of “biopersistent fibres” and “biopersistence” arose—fibres that last for a long time in the animal body are considered biopersistent and the relative time that fibres remain in the animal body is known as biopersistence. Whilst several glass systems were known to be soluble in lung fluids, resulting in low biopersistence, there was a problem in that such glass systems were generally not useful for high temperature applications. A market need was seen for a fibre that could have a low biopersistence combined with a high temperature capability.

In 1987 Johns Manville developed such a system based on a calcium magnesium silicate chemistry. Such material not only had a higher temperature capability than traditional glass wools, but also had a higher solubility in body fluids than the aluminosilicate fibres mostly used for high temperature insulation. Such low biopersistent fibres have been developed since, and a range of alkaline earth silicate [AES] fibres are now on the market including magnesium silicates, calcium silicates, and calcium magnesium silicates.

Other fibres that have been developed in recent years include alkali metal aluminosilicate fibres.

Melt formed fibres can be made by a variety of routes, but for refractory melt formed fibres the principal routes are by blowing or by spinning.

In both methods a melt of desired composition is formed and a stream of the molten material (commonly called the “tap stream”) is disrupted and accelerated to form fibres (and undesired shot).

In blowing, disruption is by a jet of high pressure air or other gas that breaks up the tap stream.

In spinning disruption is by one or more high-speed rotors (with or without blowing air around the rotor), such that fibres are flung off the rotors and collected for subsequent processing. A rotor may, for example, be a wheel or a drum, and may have a cylindrical, conical, or otherwise profiled periphery and it is commonplace to provide multiple rotors.

In blowing, disruption of the tap stream takes a very short time (e.g. 2 ms) which results in relatively uniform fiberisation. In spinning, disruption of the tap stream takes a longer time (e.g. 10 ms) during which the melt loses heat to the rotors.

The result of these different forming processes is that generally, for a given chemistry, for a mass of fibres as formed during fiberisation and before any processing:

-   -   blown fibres have a higher proportion of fine fibres than spun;     -   blown fibres have a narrower spectrum of fibre diameter than         spun fibres;     -   blown fibres have a higher amount of shot than spun fibres;     -   blown fibres are shorter on average than spun fibres.

For an aluminosilicate fibre (52-58% SiO₂; 42-48% Al₂O₃; <2% others—RCF), FIG. 6 shows a fibre diameter distribution for blown and spun materials showing blown material having the bulk of the fibres clustered around 1 μm diameter and the spun fibres having a much broader distribution. The thermal conductivity at 1000° C. of a 128 kg·m⁻³ blanket for spun material was around 0.34 W·m⁻¹·K⁻¹ whereas for blown material it was around 0.30 W·m⁻¹·K⁻¹ showing the beneficial effect of the finer diameter fibre distribution of blown fibre, despite more shot.

Typical fibre length ranges for blown RCF fibres lie in the range up to 10 cm, and for spun fibres 1-50 cm. Typically, in the spinning process, long plumes of fibre are seen with the plumes being up to a meter long

Because of the nature of the molten material, alkaline earth silicate fibres are not blown since extremely low fibre yields and high shot contents are obtained.

Fibre lengths are difficult to measure and so generally proxies for fibre length are used such as a “beaker value” [which looks at settling behaviour in a liquid] or by making blanket and measuring tensile strength.

Typically, when making blankets, the fibres are collected on a conveyor to form a mass of fibres carrying any shot present (a “fleece”), and are then, while travelling on the conveyor, “needled” to entangle the fibres to produce a blanket held together by the entangled fibres. Other methods of producing entanglement are known [for example by using fine water jets] and the present invention is not limited to use of needling.

A spinning apparatus is described in WO92/12939 and WO2015/055758 comprising

-   -   a source of molten material;     -   a spinning head comprising one or more rotors each having an         axis of rotation, the spinning head being configured to receive         molten material from the source of molten material;     -   a plurality of nozzles disposed around at least part of the one         or more rotors, configured to supply a stream of gas;     -   a conveyor disposed to receive fibres produced from the molten         material

In that apparatus the fibre produced discharges straight onto a conveyor, and below the spinning head is a pit into which shot (“pearls”) and some fibre falls and is removed for recirculation.

In WO2015/055758 the spinning head comprises rotors providing accelerations at their periphery in the range 20-400 km·s⁻², and the stream of gas has a velocity of 100-300 m·s⁻¹.

U.S. Pat. No. 4,238,213 disclosed that use of high spinning speeds favours formation of finer fibres from a spinning process. US2012/247156 indicates that forming alkaline earth silicate fibres with over 70% silica is a problem due to an increase in viscosity of the raw material so that fine fibres (<5 μm) are not obtainable, and that using a high speed rotor, with a stable supply of molten material, and at a temperature providing a defined viscosity can provide fine fibres having a low shot content. US2012/247156 states that a content of shot having a dimension of 45 μm or more of 65% or less (e.g., 30 to 55%) is achievable: however the only examples given show a shot content of 40-50%; and the demonstrated fibre diameters are above 2.5 μm.

A commercially available alkaline earth silicate fibre SUPERWOOL® PLUS, (made by proprietary technology) has a classification temperature of 1200° C. (EN 1094-1) and has:

-   -   a typical composition comprising in weight percent

SiO₂  64-66% CaO 27-31 MgO 4-7 Al₂O₃ <0.8 Others (including Al₂O₃) <1. 

-   -   “Other” in the above context means any other material and         typically these comprise oxides although other materials (e.g.         fluorides) may be present.     -   a shot content below 40 weight %, typically 35-38%     -   fibre diameters in the range 2.5-3 μm         and in the form of a 25 mm thick blanket of density 128 kg·m³     -   has a tensile strength of 75 kPa and a thermal conductivity at         1000° C. (ASTM C201) of around 0.25-0.29 W·m⁻¹·K⁻¹.

SUPERWOOL® PLUS thus already has the low shot content (38% maximum) and fine fibre diameters (2.5-3 μm) sought by US2012/247156.

Another commercially available alkaline earth silicate fibre for use at higher temperatures is SUPERWOOL® HT (made by proprietary technology), which has a classification temperature of 1300° C. (EN 1094-1) and has:

-   -   a typical composition comprising in weight percent

SiO₂ 73-74.5 wt % CaO 22.2-26 wt % MgO 0.4-0.8 wt % Al₂O₃ 0.9-1.4 wt % K₂O 0.5-0.8 wt %

-   -   with any other components or impurities amounting to at most 0.3         wt %.     -   a shot content below 50 weight %, typically 45-48%     -   fibre diameters in the range 3-3.5 μm arithmetic mean

and in the form of a 25 mm thick blanket of density 128 kg·m³ has a tensile strength of 75 kPa and a thermal conductivity at 1000° C. (ASTM C201) of around 0.34 W·m⁻¹·K⁻¹.

Known aluminosilicate fibres include not only those that are of relatively high purity, but also those with extensive impurity levels, or where additives are included to improve refractoriness or other properties. As an example of fibres that include extensive additives, Cerachem® fibres comprise ˜35% Al₂O₃, ˜50% SiO₂, and ˜15% ZrO₂.

Although methods for reducing shot from bulk fibre are known, and are used in particular to provide fibres for forming vacuum formed products from such fibres, these methods result in severe shortening of the remaining fibre. [In the following the process of mechanically removing shot from fibres is referred to as “deshotting” and the resultant fibres as being “deshotted” ].

Since the tensile strength of a blanket is dependent (among other things) on the length of the fibres, blankets made from deshotted fibres are not commercially available in blanket form, or acceptable for such use, as they show low tensile strength, and in addition the further processing steps of deshotting add to cost.

Accordingly, there is a demand for masses of fibres having a suitable length distribution and shot content to enable them to be formed into blankets of adequate strength providing lower thermal conductivities at a given density than previously achieved. Further, there is a demand for masses of fibres having a low shot content that can be chopped or otherwise processed to form low shot mass of defined characteristics.

In the applicant's previously filed application PCT/EP2017/050506 new designs of the fibre spinning apparatus were disclosed that permit the formation of low shot melt formed fibres without the necessity of a deshotting step.

SUMMARY OF THE INVENTION

The present disclosure provides a needled blanket comprising melt-formed inorganic fibres having an overall composition in weight percent

SiO₂: 47 to 65% Al₂O₃: 35 to 53%

-   -   the blanket having         -   a shot content, of shot >45 μm, of less than 51 wt %,         -   a specific surface area (BET)>0.25 m²·g⁻¹.

The SiO₂ content is preferably between 48 and 62 wt %, more preferably between 50 and 60 wt % and even more preferably between 52 and 59 wt %.

The specific surface area may be >0.26 m²·g⁻¹, >0.27 m²·g⁻¹, >0.28 m²·g⁻¹, >0.29 m²·g⁻¹, >0.30 m²·g⁻¹, or >0.31 m²·g⁻¹.

The shot content >45 μm is preferably less than 51 wt % for silica contents between 40 and 50 wt %; preferably shot content >45 μm is less than 45 wt % for silica contents between 50 and 60 wt %; and preferably shot content is less than 38 wt % for silica contents greater than 60 wt %.

The shot content is typically at least 20 wt % or 25 wt %, with shot cleaning processes typically required to reduce shot levels lower.

The fibre arithmetic diameter is preferably less 3.0 μm or 2.5 μm or 2.0 μm for silica contents below 60 wt %. The fibre arithmetic diameter is preferably less than 4.0 μm or 3.5 μm for silica contents less than 65 wt %.

The blanket preferably has a tensile strength to density ratio of >0.39 kPa/kg·m⁻³ or >0.43 kPa/kg·m⁻³ or >0.45 kPa/kg·m⁻³

For blanket with a silica content greater than 60 wt %, a tensile strength to density ratio is preferably >0.9 kPa/kg·m⁻³ or >1.1 kPa/kg·m⁻³ or >1.2 kPa/kg·m⁻³.

The disclosure further provides a mass of melt-formed fibres suitable for needling to provide such a blanket, and self-supporting insulating bodies, other than a needled blanket, formed from such fibres.

The fibres of the present disclosure may be formed on apparatus as disclosed in PCT/EP2017/050506 for forming melt-formed fibres, the apparatus comprising:

-   -   a source of molten material;     -   a spinning head comprising one or more rotors each having an         axis of rotation, at least one rotor being configured to receive         molten material from the source of molten material at a region         of the rotor to which melt is delivered;     -   a plurality of nozzles or slots disposed around at least part of         the one or more rotors, configured to supply a stream of gas;     -   a conveyor disposed to receive fibres produced from the molten         material; and     -   a barrier between the spinning head and the conveyor, an upper         edge of the barrier lying below a horizontal line lying in a         first vertical plane including the axis of rotation of at least         one rotor of the one or more rotors and intersecting the         intersection of the axis of rotation with a second vertical         plane orthogonal to the first vertical plane and including a         vertical line through said region, the included angle θ between         the horizontal line and a line in the first vertical plane         joining the upper edge of the barrier and the intersection of         the horizontal line and axis of rotation being in the range         40°-85°.

Apparatus as described permits lower shot versions of existing formulations to be provided. Fibre lengths from 1-50 cm are typically produced from such apparatus and the fibre distribution typically comprises some fibres (preferably at least 10%, more preferably at least 20%, even more preferably at least 30% and most preferably at least 40%) of greater than 10 cm in length, for example greater than 20 cm in length or greater than 30 cm in length.

By “a mass of melt-formed fibres” is meant a large quantity or aggregate of such fibres, including any amount from 100 grams upwards, including more than 1 kilogram, or more than 10 kilograms.

The scope of the disclosure is indicated in the Claims (which are incorporated herein by reference) but extends also to any new and inventive matter disclosed herein with reference to the following non-limitative description and drawings in which:

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of a conventional fibre forming machine

FIG. 2 is a schematic illustration of a fibre forming machine suitable for forming fibres in accordance with the present invention

FIG. 3 is a schematic diagram showing dimensions of a typical fibre forming machine

FIG. 4 shows fibre diameter distributions for an aluminosilicate fibre (RCF) produced by blowing and spinning respectively.

FIG. 5 shows the values of thermal conductivity for a number of different fibres.

FIG. 6 shows apparatus for measuring tensile strength of blanket

FIG. 7 shows schematically lines and planes used in defining the apparatus suitable for forming fibres in accordance with the present invention.

FIG. 8 shows schematically a plan view of a rotor.

FIG. 9 shows schematically a side view of the rotor of FIG. 10 and delivery of melt from a melt source to a region proximate the rotor

FIG. 10 is a summary of trials on an RCF composition

DETAILED DESCRIPTION The Fibre Forming Process

As stated above, a known process for the manufacture of inorganic fibres is to supply a stream of a molten material of the desired chemical composition to a high-speed rotor (with or without blowing air around the rotor), such that fibres are flung off the rotor and collected for subsequent processing.

The process is hypothesised to work by a droplet of molten material being flung off the rotor and drawing a “tail” of molten material that forms the fibre. The droplets form part at least of the shot.

For the process to work the viscosity of the molten material must be appropriate.

The molten material is typically held in a container having heating/insulation means to keep the molten material at a suitable temperature.

As viscosity depends upon temperature, control of the temperature of the molten material is advisable. For each material a different range of temperatures will provide the optimum viscosity. Ideally the molten material as it hits the rotor should be within ±150° C. preferably within ±100° C., and more preferably within ±50° C. of the optimum temperature for the molten material concerned. It is advantageous to monitor the temperature of the stream of molten material [e.g. using a pyrometer] as it leaves the container [and ideally as it hits the rotor] and to use this to control supply of heat to the molten material.

To ensure best performance, the stream of molten material should be uninterrupted for as long as possible during the fibre forming process. This means that the pour rate of the molten material should be sufficiently high to provide a continuous stream and not so low as to break up into droplets of molten material.

FIG. 1 shows fibre forming apparatus in which a motor arrangement 1, drives a rotor 2 housed in a fibre forming region 3 delimited at an end remote from the rotor by a barrier 4. Beyond the barrier 4 is what is conventionally known as a “wool bin” 5 where in use fibres settle onto a conveyor 6 to form a fleece of loose fibres 7 that may then be passed on to further processing [e.g. by “needling” to form a blanket]. Extractors 8 remove air from below the conveyor assisting draw down of fibre from the wool bin to the conveyor.

The apparatus also comprises a blower 9 that passes air [typically at 50 kPa or less above atmospheric] through an air ring into the fibre forming area behind the rotor 2.

The rotor arrangement which comprises two rotors 2, although a single rotor or more than two rotors may conventionally be used. As is conventional, one rotor is displaced from and placed slightly above the other, the appropriate angle of displacement and separation between the rotors 2 being a matter of design. Suitable angles and displacements are discussed, for example, in WO92/12939 and WO2015/055758 but typically the rotors have a separation of [2-10 mm] and the angle between horizontal and a line connecting the axis of one rotor to the axis of the other rotor is in the range [0-15° (typically) and 2-10° (preferred)]. The entire assembly of rotors may be displaced from the vertical as in U.S. Pat. No. 4,238,213. One or more of the rotors may be mounted at one end of a drive shaft with at least two spaced bearings supporting the drive shaft within a direct drive mechanism, which may be mounted with shock absorbers in a mount.

Fibre is produced as melt is flung from the peripheries of the rotors; once it has been made it needs to be moved away from the rotors into the wool bin. This is done partially by the residual velocity of the fibre and shot, and partly by the use of gas (usually air) moving generally perpendicular to the travel of the fibres which are then transported into the wool bin. The equipment used is generically referred to as ‘air rings’ or ‘stripper rings’; the name ring comes from the shape, which forms part circles around the outside of the spinning rotors. The air ring typically comprises holes in metal blocks (typically 50-100 holes per block) with the air supply charged by a blower.

Preferably the air rings extend around as much of the periphery of the rotor as possible without disrupting the melt stream. For example, for a given rotor the air ring may extend around >180°, >200°, >220°, or >240° of the rotor periphery.

In operation melt drops as a melt stream from a source of molten material 25 [FIG. 11] onto the rotor 2 and is spun off to form fibres, fibre formation being assisted in part by the air flow from blower 9. Melt sources can comprise any type appropriate to the nature of the material being melted. This is conventional technology and exemplified, for example, in US2012/0247156.

Typically melt sources comprise a chamber for melting and holding molten the constituents of the melt and a tapping hole in the base of the chamber to permit the melt to be released when required. In practice, point-like precision of impact of the melt on the rotor is not possible, and cone 26 from the source 25 to the region 23 indicates a range of possible melt stream paths, such that the melt can land on the rotor over a region 23. The melt stream is shown schematically as a dotted line 20 representing a vertical line through the region 23. The vertical line 20 may pass anywhere through region 23, for example through the centroid of region 23 on the rotor, and where melt is delivered vertically from an orifice 27 in the source of molten material 25, the vertical line 20 may conveniently pass through the centroid of the melt delivering orifice 27.

In practice, since the melt stream may lie off this vertical line anywhere within the region 23, it may prove necessary to arrange for the rotor to be movable to ensure the melt stream falls on the optimum position for the melt in question. Typically, the melt is preferred to impinge on the first rotor it meets, on the front half of the rotor [e.g. between ¼ and ½ the depth of the rotor from the front (conveyer facing) face of the rotor and to impinge within 0-90°, typically 18-72° (e.g. 18-30°) of a vertical plane including the rotor axis either in advance or behind the direction of rotation of the rotor. The size of the region 23 will depend upon the geometry of the source 24 and its position relative to the rotor.

Fibres produced from the melt are carried by the stream of gas from the rotors to pass over the upper edge of the barrier 4 towards the conveyer 6; while shot and short fibre falls back from the lip of the barrier 4 to a waste chute 10 (sometimes called the “shot pit”) from which the waste shot and fibre passes to a granulator which breaks up the waste preparatory for disposal or re-use.

The applicant previously considered the slope from the upper edge of the barrier 4 to the waste chute 10 to be a region where further shot and fibre separation could occur, with the fibre being blown up the slope to the upper edge of the barrier 4.

Such apparatus typically produces fleece with a shot content of 45-50% assuming all other parameters (e.g. tap stream temperature and pour rate are optimal).

A problem with this apparatus is that the use of a low pressure air system implies high volumes of air to strip the fibres from the rotor and this leads to turbulence and eddying within the waste chute 10 such that some shot initially stopped by the barrier 4 can be blown up the slope of the barrier 4 and into the wool bin 5.

The applicants have realised that by lowering the upper edge of the barrier relative to the rotor and shortening the distance from the rotor to the barrier, there is a lower chance of eddying such that shot and short fibre falling from the barrier towards the waste chute is less likely to be blown back over the barrier.

FIG. 2 shows fibre forming apparatus in accordance with the present invention in which like integers carry the same reference signs as FIG. 1.

In this apparatus rather than a blower 8, compressed gas under high pressure [typically >100 kPa above atmospheric] is supplied to a series of flat spray nozzles distributed in a ring around the rotors 2. This provides more efficient separation of the fibre and shot so that more fibre goes into the wool bin 5 and more shot drops down into the waste chute 10. A secondary blowing device is also provided under the rotors, this provides further separation of fibre and shot, but also improved flow of fibre off the barrier, and prevents fibre laden shot returning back up the ducting into the wool bin.

Suitable spray nozzles are for a flat spray pattern without hard edges. They come with several spray angles.

This process typically allows a shot content of 30-45% to be achieved for alkaline earth silicate fibres without deshotting.

FIG. 3 shows the construction of FIG. 1 with dimensions, and shows schematically the angle θ, the determination of which is shown in greater detail in FIG. 7

FIG. 7 shows the axis of rotation 16 of a rotor and a vertical plane 17 including axis 16.

Plane 17 intersects orthogonal vertical plane 18 along line of intersection 19, and vertical plane 18 includes vertical line 20 which passes through the region 23 on the rotor to which melt is delivered.

Line 21 lies within plane 17 and extends from the intersection of axis of rotation 16 with plane 18 to the upper edge of the barrier 4.

Horizontal line 22 lies within plane 17 and meets the intersection of axis of rotation 16 with plane 17. [When the axis of rotation 16 is horizontal, lines 16 and 22 are identical]. The angle θ is the angle between line 21 and horizontal line 22,

FIG. 8 shows schematically in plan the rotor 2 positioned by the back 24 of the apparatus and the barrier 4. The region 23 may lie in advance or behind top centre in the direction of rotation of the rotor 2.

Table 1 compares the apparatus of FIG. 1 with the apparatus of FIG. 3.

TABLE 1 Apparatus of Apparatus of Dimension FIG. 1 FIG. 2 A - Length from end to end 9030 mm 10600 mm B - Height of barrier below roof 1183.8 mm 1400 mm C - Height of conveyor below 3790 mm 3900 mm roof D - Length of conveyor internal 6467.2 mm 9350 mm of wool bin E - Distance from conveyor to 1353.7 mm 750 mm mouth of waste chute F - Width of base of waste 825.8 mm 525 mm chute G - width of mouth of waste 1166.3 mm 525 mm chute H - Height of rotor axis below 435 mm 435 mm roof J - Distance of barrier from 1817.4 mm 600 mm rotor end of apparatus K - Distance from vertical line 275 mm 275 mm through centre of region 23 to back end of apparatus B-H - Height of rotor centre 748.8 mm 965 mm above barrier Θ 26.8° 74.6° Gas stream velocity 16-17 m · s⁻¹ 55-100 m · s⁻¹

The principle difference between the designs is the increase in the angle θ from below 30° to above 40° and the higher air velocity (above 40 m·s⁻²). This difference results in a lower shot content for fibres of a given chemistry produced on the Apparatus of FIG. 2 than the Apparatus of FIG. 1.

In addition, the increased angle can be achieved by bringing the upper edge of the barrier closer to the rotor and in consequence permits a longer conveyor to be used for a given overall length of the wool bin. This longer conveyor improves uniformity of lay down of fibre.

The improvements achieved for a given chemistry, tap stream temperature, and rotor speeds are indicated below with reference primarily to alkaline earth silicate fibres but similar improvements will apply to other chemistries [including, without limitation, aluminosilicate chemistries, alkali metal aluminosilicates]. The following indicates some of the relevant variables that need to be considered in providing optimal fibre production.

Tap Stream Temperature.

The optimal value is chemistry dependent.

For the present aluminosilicate chemistries the tap stream temperature is preferably in the range 1950-2200° C.

Pour Rate.

The optimal pour rate depends upon the capacity of the rotor to convert the tap stream into fibre and ensuring a stable tap stream. For 20 cm (8″) rotors good results are typically obtained with a pour rate between 250 kg/hr and 800 kg/hr. Below 250 kg/hr the tap stream tends to break up, and the resultant “splatter” creates damaging shot. Preferably, for such rotors, the pour rate is 400-750 kg/hr.

Rotor Speed.

For 20 cm (8″) rotors this is preferably 15000-17000 rpm [equivalent to accelerations of about 250-320 km·s⁻²] although higher rotational speeds can result in finer fibre. This is substantially greater than 12000 rpm, which is the usual speed for making alkaline earth silicate fibres and equivalent to about 160 km·s⁻². Results for alkaline earth silicate fibres when speed is below 10000 rpm [equivalent 110 km·s⁻²] are less beneficial; although aluminosilicate fibre (RCF) is typically made at 10,000 rpm.

Blankets formed using fibres produced under these spinning conditions using the apparatus claimed possess lower thermal conductivity and shot content than fibres produced at slower linear speeds and retain acceptable mechanical properties such as tensile strength. As an indication, Table 2 shows typical tensile strengths and shot contents of blankets of various density formed from specified fibres:

TABLE 2 Alkaline earth silicate fibre (calcium magnesium silicate fibre of SUPERWOOL ® Composition Aluminosilicate fibre PLUS composition) Blown or spun Blown Spun Spinning apparatus N/A Apparatus of FIG. 1 Apparatus of FIG. 2 Spinning speed [all with N/A 12,000 rpm 15,000 rpm 20.3 cm (8″) rotors]) Tensile Density of 17 kPa >25 kPa >25 kPa >25 kPa 25 kPa strength blanket 31 kPa >45 kPa >40 kPa >40 kPa 55 kPa  64 kg/m³ 44 kPa >60 kPa >50 kPa >50 kPa 55 kPa  96 kg/m³ 128 kg/m³ Average shot >45 μm* 50% 50% 50% 35-38% 28-35% typical typical typical typical Typical arithmetic mean <2 2.5-3 2.5-3 2.5-3 <2 fibre diameter [μm] Typical thermal    0.30 0.34 0.38 0.29 0.21 conductivity at 1000° C. [W · m⁻¹ · K⁻¹] *Under ISO guidelines 10635 for fibre making provide that the testing party may declare what value they are using. For the purpose of this application, shot comprises any particulate material that is over 45 μm in size

As can be seen from the table:

-   -   the tensile strength for spun fibre blankets are significantly         higher than for blown fibre blanket, this significantly helps in         handling     -   moving from Apparatus of FIG. 1 to Apparatus of FIG. 2 results         in a major drop in shot content and correspondingly lower         thermal conductivity     -   increasing the spinning speed results in a much lower thermal         conductivity since fibres of diameter comparable with blown         fibres can be achieved with a lower shot content.

Further details are set out in the following examples and comparative examples.

The products of Comparative Examples 1 and 2 are claimed in applicant's previously filed application PCT/EP2017/050506 and do not form part of the present invention.

Comparative Example 1

Calcium magnesium silicate fibres of chemistry indicated in Table 3 were produced in apparatus as shown in FIG. 2 with the dimensions given in Table 1 using a tap stream at a temperature of 1450±50° C. directed to on 20.3 cm [8″ ] diameter rotor rotating at a speed of 15,000 rpm. Table 3 compares the chemistry of Example 1 with typical composition of SUPERWOOL® PLUS and shows typical measured properties:

TABLE 3 Example 1 SUPERWOOL ® PLUS Component Amount in wt % CaO 30.1 27-31 MgO 5.4 4-7 SiO₂ 64.6 64-66 Property Arithmetic mean diameter 1.85 μm     3-3.5 μm Cumulative total for shot 29-33%  35-38% 45 μm or above

The thermal conductivity for a blanket, formed from the fibres of Example 1, with density 125.4 kg·m⁻¹·K⁻¹ is shown in Table 4 and is a significant improvement over SUPERWOOL® PLUS blanket which has a typical value at 1000° C. of 0.25-0.29 W·m⁻¹·K⁻¹.

TABLE 4 Commercial Temperature SUPERWOOL ® PLUS % (° C.) Sample (datasheet values) difference 200° C. 0.04 0.05 20% 400° C. 0.06 0.08 25% 600° C. 0.10 0.12 17% 800° C. 0.15 0.18 17% 1000° C.  0.21 0.25 16% 1100° C.  0.24 n/a

Comparative Example 2

Calcium magnesium silicate fibres of chemistry indicated in Table 5 were produced in apparatus as shown in FIG. 1 with the dimensions given in Table 1 using a tap stream at a temperature of 1680-1730° C. directed to on 20.3 cm [8″ ] diameter rotor rotating at a speed of 15,000 rpm. Table 5 compares the chemistry of Example 2 with typical composition of SUPERWOOL® HT and shows typical measured properties:

TABLE 5 Example 2 SUPERWOOL ® HT Component Amount in wt % CaO 24.68 22.2-26  Al₂O₃ 1.18 0.9-1.4 K₂O 0.77 0.5-0.8 MgO 0.6 0.4-0.8 SiO₂ 72.72  73-74.5 Property Arithmetic mean diameter 1.85 μm     3-3.5 μm Cumulative total for shot 33.24% 38.25% 45 μm or above

The thermal conductivity for a blanket with density 117.5 kg·m⁻¹·K⁻¹ is shown in Table 6 and compares well with a typical value at 1000° C. of 0.34 W·m⁻¹·K⁻¹ for SUPERWOOL® HT.

TABLE 6 Conductivity (W/m · K) Commercial Temperature SUPERWOOL ® HT % (° C.) Example 2 (datasheet values) difference 200° C. 0.04 0.04  0% 400° C. 0.07 0.08 13% 600° C. 0.11 0.14 21% 800° C. 0.18 0.23 22% 1000° C.  0.26 0.34 24% 1200° C.  0.37 0.48 23%

It is known that the thermal conductivity of a blanket also depends on density of the blanket, and FIG. 5 shows the commercial literature values of thermal conductivity against blanket density for SUPERWOOL® PLUS and SUPERWOOL® HT and the blown and spun RCF fibres described above, together with the experimental values for Examples 1 and 2.

As can be seen the fibres produced using the apparatus of FIG. 2 with a rotor giving an acceleration of about 250 km·s⁻² produces significantly lower thermal conductivities than commercial product and indeed lower than blown RCF.

The fibres can be used to produce an insulating blanket of thermal conductivity <0.21 W·m⁻¹·K⁻¹ at 1000 C and 128 kg/m³ density. This is possible due to the properties of the fibres—fine, low shot, with extremely low thermal conductivity in their own right.

Density of a blanket also correlates with the thermal mass of the blanket, which is of particular importance in cycling conditions. By providing a required thermal conductivity with a lower density blanket than a conventional blanket of equivalent composition, the present invention reduces the thermal mass of the blanket.

If the lines for SUPERWOOL PLUS and SUPERWOOL HT respectively in FIG. 5 are extrapolated to the thermal conductivities shown for Examples 1 and 2 respectively, densities of 20 kg/m⁻³ or more above those of Examples 1 and 2 would be indicated as necessary for the same thermal conductivity.

Prior to the development of the apparatus disclosed herein production of such blankets was impossible: whilst shot could conceivably be removed from fibres produced via another method, the shot cleaning operation shortens the fibres, making them unsuitable for the production of a blanket.

Example 3

An aluminosilicate fibre was trialled on spinning apparatus as shown in FIG. 2 using pairs of 20 cm (8″) rotors, and the rotor speed increased stepwise from 9000/9500 rpm (one rotor at 9000, the other at 9500 rpm) through to both rotors running at 15,000 RPM. Fibre diameter and shot content were measured and the results and fibre composition are set out in FIG. 10.

With increasing rotor speed both fibre diameter and shot content decreased to provide, at higher speeds, fibres having fibre diameters similar to blown RCF, but shot content similar to or significantly less than spun RCF.

In light of the results of Example 3 the applicants have compared:

-   -   aluminosilicate materials made with the presently claimed         apparatus using the rotor configuration of Example 3 and high         rotor speeds (both rotors at 14,500 rpm); with, materials made         using the presently claimed apparatus using lower rotor speeds     -   commercially available materials.

Example 4

A “standard” spun refractory ceramic fibre has a typical composition in weight percent:

-   -   Alumina 46-48%     -   Silica 52-54%         and is exemplified by Cerablanket™ (a trademark of Morgan         Advanced Materials plc). Such a material has a shot content >45         μm of about 50%.

A material of the same composition made using the high rotor speeds (both rotors at 14,500 rpm) has a shot content >45 μm of 43-46%.

Comparative results for thermal conductivity for a 128 kg/m³ blanket measured by ASTM-C201 expressed in W/mK are shown in Table 7.

TABLE 7 Thermal Conductivity (W/m · K) Temperature Example Morgan Cerablanket ™ % (° C.) 4-14500 rpm RCF (data sheet) difference 200 0.06 0.06  0% 400 0.08 0.1 20% 600 0.12 0.15 20% 800 0.17 0.2 15% 1000 0.23 0.27 15%

Example 5

Blown fibres tend to be finer than spun fibres, and to hence provide lower thermal conductivity. However blown fibres tend to be shorter than spun fibres and blankets are difficult to make from blown fibres. Blown fibres also tend to have more shot than spun fibres. Typically blown RCF has a shot content >45 μm of above 50%, and above a spun fibre of like composition.

High alumina (HA) RCF fibre is known for meeting higher temperature applications than standard RCF fibre and is normally blown, as it has proven difficult in the past to spin or make into blanket.

HA fibres have typical compositions in weight percent:

Alumina 50-53% Silica 47-50%

Comparative results for thermal conductivity for a 128 kg/m³ blanket measured by ASTM-C201 expressed in W/mK are shown in Table 8, which compares:

-   A. a spun HA fibre with composition based on

Alumina 50-52% Silica 48-50%

-   -   made using the high rotor speeds (both rotors at 14,500 rpm)         having a shot content >45 μm of 43-46%.

-   B. a “standard” blown refractory composition [Kaowool® a trademark     of Thermal Ceramics, Inc.] with composition in weight %

Alumina 46-48% Silica 52-54%

-   -   With some substitution of up to 3% alumina by iron and titanium         oxides.

-   C. a commercial HA product with composition based on Alumina 53%,     Silica 46%, balance impurities.

As can be seen, spun fibres of a high alumina composition RCF produced on the apparatus of the present invention, are superior in thermal conductivity to blown RCF fibres whether of standard or high alumina composition.

TABLE 8 Thermal Conductivity (W/m · K) A B High speed Kaowool ® C % % Temperature “HA” spun “standard” RCF Commercial difference difference ° C. fibre blown blanket blown blanket from B from C 200 0.05 0.05 0.07  0% 29% 400 0.08 0.1 0.11 20% 27% 600 0.13 0.15 0.17 13% 24% 800 0.19 0.2 0.24  5% 21% 1000 0.27 0.3 0.33 10% 18% 1200 0.36 0.39 0.44  8% 18%

A factor that is important for making blanket is its tensile strength. For a given composition, short fibres make weaker blanket than long fibres. The applicants have made needled blankets at a density of about 128 kg·m⁻³ from a range of RCF compositions as indicated in Tables 9 & 10 below.

TABLE 9 Experiment/Comparative Experiment 1 C-1 2 C-2 C-3 Chemistry Alumina (%) 42.28 45.97 50.22 49.85 48.95 Silica (%) 57.23 53.77 49.24 49.31 50.44 Spinning speed (rpm) 15000 12500 14500 13000 13000 Shot content 45 μm 40.8 51.6 50.6 60.2 57 Tensile strength (kPa) 71.7 71 26.9 20 27.6 Tensile strength/density 0.56 0.55 0.21 0.16 0.22 kPa/kg · m⁻³ Diameter (μm) 2.1 2.8 2.8 3.7 3.1 SSA (BET) 0.317 0.220 0.254 0.201 0.237 Thermal  200° C. 0.05 0.05 0.05 0.05 0.05 conductivity  400° C. 0.08 0.07 0.08 0.08 0.08 (W/mK)  600° C. 0.12 0.12 0.13 0.13 0.13  800° C. 0.16 0.17 0.19 0.19 0.19 1000° C. 0.22 0.25 0.27 0.27 0.26

TABLE 10 Sample reference C-4 3 Chemistry Alumina (%) 34.7 35.0 Silica (%) 64.3 64.7 Spinning speed (rpm) 12000 13500 Shot content 45 μm 35.7 32.6 Tensile strength (kPa) 137 138 Tensile strength/density 1.12 1.18 kPa/kg · m⁻³ Diameter (μm) 3.63 3.61 SSA (BET) 0.232 0.296 Thermal  200° C. 0.05 0.06 conductivity  400° C. 0.08 0.08 (W/mK)  600° C. 0.14 0.13  800° C. 0.22 0.20 1000° C. 0.32 0.29

It is a feature of the tensile strength test used that blankets having a sufficient proportion of long fibres (sufficient to span the 150 mm clamping distance) show a higher tensile strength than blankets without such long fibres. The significant drop from ˜70 kPa for experiment 1 and comparative experiment C-1 to less than 30 kPa for experiment 2 and comparative experiments C-2 and C-3 shows that these latter fibres, with a silica content below 52 wt %, are significantly shorter than the former fibres, with a silica content in the 53-58 wt % range.

Likewise, the tensile strength of experiment 3 and comparative experiment C-4, with a silicate content of 64 wt % indicate a further increase in tensile strength.

The blankets/fibres within the scope of the present invention (experiments 1 to 3) demonstrate that use of high spinning speeds (at a specific fibre composition) results in both lower shot and generally finer fibres, with the process providing a higher specific surface area compared to fibres produced at lower speeds as indicated in comparative experiments C-1 to C4).

As indicated in the Tables 9 & 10, an increase in silica content is accompanied by a decrease in shot levels. The specific surface area was able to be maintained at different compositions, with the fibre diameter generally increasing with silica content (at the comparable spinning speeds), particularly for silica contents greater than 52 wt %.

Therefore, the compositions of the present invention are able to provide an advantageous balance of strength and thermal insulation through converting a high portion of the molten aluminosilica glass to fibre rather than shot.

The applicants have shown that a variety of aluminosilicate fibres (e.g. refractory ceramic fibres [RCF]— also known as aluminosilicate wool [ACW]) can be made using the methods and apparatus described herein to provide fibre masses of fibre diameter comparable to blown fibre, with fibre length comparable to spun fibre, and with low shot content. Such materials will be useful in many applications, including in automotive applications as further mentioned below.

One application to which such fibres may be applied is to monolithic refractory modules, for example the product known as PYRO-BLOC® which is a needled body of lubricated fibres with typical densities of the order of 160-240 kg·m⁻³. Such modules are used in a variety of applications. Fibres of a nature suitable to form blankets as now claimed, particularly blankets having a tensile strength to density ratio of >0.39 kPa/kg·m⁻³, enables monolithic refractory modules to be made having

-   -   a shot content, of shot >45 μm, of less than 51 wt %,     -   a specific surface area (BET)>0.25 m²·g⁻¹         or even better; for example having     -   a shot content, of shot >45 μm, of less than 45 wt %, and/or         having     -   a specific surface area (BET)>0.26 m²·g⁻¹, >0.27 m²·g⁻¹, >0.28         m²·g⁻¹, >0.29 m²·g⁻¹, >0.30 m²·g⁻¹, or >0.31 m²·g⁻¹

Tensile strength for such monolithic refractory modules need not (and is not) be as high as for blanket. Tensile strengths in excess of 5 kPa, or 10 kPa, or 20 kPa, or 30 kPa are expected to give functional modules and even lower may work in some applications. Measurement may be by cutting a sample of like size to blanket (as indicated below under test methods) and with a thickness of 25 mm with general fibre alignment in the plane of the sample; burning off lubricant at, say, 650° C., and measuring as below.

Test Methods Shot Content

Shot content is measured by a jet sieve method using a Hosokawa Micron Air Jet Sieve (from Hosokawa Micron Powder Systems).

To ensure that the fibres pass through the sieve, the sample has to be prepared by crushing, this breaks the fibres to short lengths which are no longer tangled together in clumps that otherwise might be mistakenly measured as shot. The jet sieve then uses ultrasonic energy to agitate the fibres and align them with the mesh of the sieve. Suction then pulls the fibres through and collects them in a high efficiency particulate arresting (HEPA) filter. By measuring the weight of the sample before and after sieving, the proportion of shot can be calculated.

In detail:

Heat Treatment of Sample

To avoid moisture, or lubricants or other organic materials causing fibres to aggregate into “lumps”; preheating to an appropriate temperature for the sample [e.g. to 650° C.) to dry and/or burn off any lubricant/organic is appropriate if the sample is not known to be free of such materials.

Some materials may be too tough to be readily crushed in the following step, if so, heat treating to embrittle the fibres may be required.

The need for such heat treatment may be assessed by attempting the following steps and viewing the sample after sieving to determining whether sufficient fibrous material is retained in the sieve to affect the outcome of the measurement by more than the desired level of precision.

Crushing

Samples need to be crushed to break up the fibre tangles and to separate the shot from the fibre as well as to make the sections short enough to pass through the sieves' mesh. This has to be done in a manner that provides efficient shortening of the fibres without affecting the nature of the shot significantly.

Samples (typically 50-100 g or whatever size is appropriate for the die used) are crushed three times in a die at a minimum of 10 MPa (preferably at about 12 MPa). Between crushes the samples are well stirred to break up lumps and compacts so that the subsequent pressing can work on any uncrushed material.

Most samples will be crushed sufficiently by this process, but further repetition may be required for “obstinate” samples. The need for further repetition for a particular material, or higher crushing pressures, can be assessed by viewing the sample after sieving to determining whether sufficient fibrous material is retained in the sieve to affect the outcome of the measurement by more than the desired level of precision.

Weighing

A balance is used that meets or exceeds the following specification (e.g. Sartorius MSE1202S-100-DO)

-   -   Readability 0.01 g     -   Repeatability 0.005 g     -   Linearity 0.02 g     -   Range 0-800 g

The balance pan must also have a diameter > the sieve diameter and must be placed on a solid base to minimise vibrations.

The lid and sieve used (see below) are first weighed and then an appropriate amount of crushed sample is added, typically 20±0.5 g, measured to the nearest 0.01 g.

Sieving

Suitable apparatus comprises a Hosokawa Micron air jet sieve and lid; a Nilfisk GD930 vacuum cleaner; and a Stainless steel test sieve (BS410) designed for air jet sieve. For determining shot content as reported herein a 45 μmicron sieve was used. Any suitable jet sieve may be used.

Sieving with this apparatus comprises the steps:

-   -   putting the lid on to the sieve,     -   placing the sieve on the jet sieve unit, and sealing thereto     -   using a sieving time of 180 seconds under a reduced pressure of         at least 4.7 kPa (19 inches of water),         during the sieving, if necessary, stopping sieving to brush off         any material adhering to the lid through static electricity

After sieving the sieve, lid, and retained shot are measured together and the amount of shot determined by difference.

Tensile Strength

Tensile strength is measured by a modification of ISO 10635:1999(E). The parting strength of a blanket is determined by causing rupture of test pieces at room temperature.

Samples are cut using a template (230±5 mm×75±2 mm). The samples are dried at 110° C. to a constant mass, cooled to room temperature and then measured and tested immediately.

The width is measured using a steel rule to a 1 mm accuracy across the middle of the piece and the thickness of the sample is measured on each sample (at both ends of the sample) using the EN1094-1 needle method.

Samples for each test are taken along the direction of manufacture.

The samples are clamped at each end by clamps comprising a pair of jaws having at least 40 mm×75 mm in clamping area with serrated clamping surfaces to prevent slippage during the test. These dimensions give an unclamped span of 150±5 mm to be tested. The clamps are closed to 50% of the sample thickness (measured using a Vernier caliper or ruler).

The clamps are mounted in a tensile testing machine [e.g. Instron 5582, 3365 using a 1 kN load cell, or a machine of at least the equivalent functionality for testing tensile strength]

The crosshead speed of the tensile testing machine is a constant 100 mm/min throughout the test.

Any measurement with the sample breaking nearer to the clamp jaw than to the centre of the sample is rejected. FIG. 8 shows the sample before and after testing for a good test.

The maximum load during the test is recorded to allow strength to be calculated.

Tensile strength is given by the formula:

${R(m)} = \frac{F}{W \times t}$

Where:

-   -   R(m)=Tensile Strength (kPa)     -   F=Maximum Parting Force (N)     -   W=Initial Width of the active part of the test piece (mm)     -   T=Initial Thickness of test piece (mm)

The test result is expressed as the mean of five tensile strength measurements together with the bulk density of the product.

Fibre Diameter

Fibre diameter can be measured in a variety of ways. A suitable method, used in determining the values presented herein comprises:

Sample Dispersion

Homogeneously dispersing a suitable quantity of fibre sample onto a 25 mm carbon tab (a carbon based electrically conductive adhesive disc, frequently referred to as a Leit tab) mounted on a 32 mm aluminium SEM stub. Dispersion is preferably by a dry method to reduce agglomeration. A convenient product to use is a Galai PD-10 powder disperser which uses a vacuum to such fibre into a chamber, from where it deposits onto the stub surface. By suitable quantity is meant sufficient to provide a uniform coating on the stub, but not a coating so dense as to make measurement problematic [e.g. 0.03 to 0.3 grams].

Sputter Coating

Coating the sample with a conductive material (e.g. metal or carbon).

Imaging

Using a scanning electron microscope (SEM) to take a number of images from regions of the sample [e.g. 50, 100, 200 or more images], the images comprising a number of fibres. Typically anywhere from 100 to 300 fibres would be measured. For the purpose of reproducibility, 300 fibres from at least 50 different images may be measured.

Image Analysis

For each image any fibre that is in focus, has an aspect ratio (length/diameter) of at least 3:1 and touches a reference line placed across the image, the diameter is measured by measurement from the SEM image.

This part may be semi-automated using image analysis software linked to the SEM. such as the Scandium® system available from Olympus Soft Imaging Solutions GmbH.

From the accumulated fibre measurements calculate the arithmetic mean diameter.

Because the diameter is measured only for fibres intercepting a line, and the probability of interception depends on fibre length, this method provides a length weighted arithmetic mean diameter.

Specific Surface Area

An alternative measure that correlates with fibre diameter (and is quicker to use) is to look to the specific surface area.

The lower the shot content, the better the correlation between SSA and fibre diameter.

There are various methods of measuring specific surface area, the most commonly applied being the Brunauer, Emmett and Teller (BET) method. Specific surface areas mentioned in this disclosure were measured using a Micrometrics TriStar 3000 apparatus. Samples were preheated to 650° C. to burn off any lubricant or other volatile material that might impede measurement. Samples were degassed at 350° C. in a nitrogen atmosphere.

Density

Using a dried sample (as provided for measurement of tensile strength above), the width is measured using a steel rule to a 1 mm accuracy across the middle of the piece and the thickness of the sample is measured on each sample (at both ends of the sample) using the EN 1094-1 needle method. Length is measured end-to-end using a steel rule to a 1 mm accuracy and volume calculated from length, width and thickness. The blanket is weighed and density taken as measured mass divided by calculated volume.

Potential Uses

The fibres of the present invention can be used, subject to meeting relevant performance criteria, for any purpose for which fibrous inorganic materials, and particularly alkaline earth silicate and aluminosilicate materials, have been used heretofore; and may be used in future applications where the fibre properties are appropriate. In the following reference is made to a number of patent documents relating to applications in which the fibres may be used, subject to meeting relevant performance criteria for the application. The fibres of the present invention can be used in place of the fibres specified in any of these applications subject to meeting relevant performance criteria. The fibres may be used as made or in processed form [for example as chopped fibres] to meet the demands of the application concerned.

For example, the fibres may be used as:

-   -   bulk materials;     -   in a mastic or mouldable composition [WO2013/080455,         WO2013/080456] or as part of a wet article [WO2012/132271];     -   as a constituent in needled or otherwise entangled         [WO2010/077360, WO2011/084487] assemblies of materials, for         example in the form of blanket, folded blanket modules, or high         density fibre blocks [WO2013/046052];     -   as a constituent of non-needled assemblies of materials, for         example felts, vacuum formed shapes [WO2012/132469], or papers         [WO2008/136875, WO2011/040968, WO2012/132329, WO2012/132327];     -   as a constituent (with fillers and/or binders) of boards,         blocks, and more complex shapes [WO2007/143067, WO2012/049858,         WO2011/083695, WO2011/083696];     -   as strengthening constituents in composite materials such as,         for example, fibre reinforced cements, fibre reinforced         plastics, and as a component of metal matrix composites;     -   in support structures for catalyst bodies in pollution control         devices such as automotive exhaust system catalytic converters         and diesel particulate filters [WO2013/015083], including         support structures comprising:         -   edge protectants [WO2010/024920, WO2012/021270];         -   microporous materials [WO2009/032147, WO2011019394,             WO2011/019396];         -   organic binders and antioxidants [WO2009/032191];         -   intumescent material [WO2009/032191];         -   nanofibrillated fibres [WO2012/021817];         -   microspheres [WO2011/084558];         -   colloidal materials [WO2006/004974, WO2011/037617]         -   oriented fibre layers [WO2011/084475];         -   portions having different basis weight [WO2011/019377];         -   layers comprising different fibres [WO2012065052];         -   coated fibres [WO2010122337];         -   mats cut at specified angles [WO2011067598];     -   [NB all of the above features may be used in applications other         than support structures for catalytic bodies]         -   in the form of an end cone [e.g. U.S. Pat. Nos. 6,726,884,             8,182,751]     -   as a constituent of catalyst bodies [WO2010/074711];     -   as a constituent of friction materials [e.g. for automotive         brakes [JP56-16578]];     -   for fire protection [e.g. WO2011/060421, WO2011/060259,         WO2012/068427, WO2012/148468, WO2012/148469, WO2013074968]; and         optionally in combination with one or more intumescent         materials, endothermic materials, or both intumescent and         endothermic materials     -   as insulation, for example;         -   as insulation for ethylene crackers [WO2009/126593],             hydrogen reforming apparatus [U.S. Pat. No. 4,690,690];         -   as insulation in furnaces for the heat treatment of metals             including iron and steel [U.S. Pat. No. 4,504,957];         -   as insulation in apparatus for ceramics manufacturing.

The fibres may also be used in combination with other materials. For example the fibres of the invention may be used in combination with polycrystalline (sol-gel) fibres [WO2012/065052] or with biosoluble fibres [WO2011/037634].

Bodies comprising the fibres may also be used in combination with bodies formed of other materials. For example, in insulation applications, a layer of material according to the present invention [for example a blanket or board] may be secured to a layer of insulation having a lower maximum continuous use temperature [for example a blanket or board of alkaline earth silicate fibres] [WO2010/120380, WO2011133778]. Securing of the layers together may be by any known mechanism, for example blanket anchors secured within the blankets [U.S. Pat. No. 4,578,918], or ceramic screws passing through the blankets [see for example DE3427918-A1].

The unique control of shot content and fibre diameter provided by the method and apparatus disclosed provides fibre masses that with little or no need for post-formation deshotting, enable products to be made with lower thermal conductivity than current comparable products on the market.

The above disclosure is by way of example and the person skilled in the art will readily be able to find a multiplicity of uses for the fibres produced on the disclosed apparatus or by the disclosed methods. 

1. A needled blanket comprising melt-formed inorganic fibres having an overall composition in weight percent SiO₂: 47 to 65% Al₂O₃: 35 to 53% the needled blanket having a shot content, of shot >45 μm, of less than 51 wt %, a specific surface area (BET)>0.25 m²·g⁻¹.
 2. A needled blanket as claimed in claim 1, in which the amount of SiO₂ is greater than 52%.
 3. A needled blanket as claimed in claim 2, in which the amount of SiO₂ is greater than 53%.
 4. A needled blanket as claimed in claim 3, in which the amount of SiO₂ is greater than 54%.
 5. A needled blanket as claimed in claim 4, in which the amount of SiO₂ is greater than 55%.
 6. A needled blanket as claimed in claim 5, in which the amount of SiO₂ is greater than 56%.
 7. A needled blanket as claimed in claim 6, in which the amount of SiO₂ is greater than 57%.
 8. A needled blanket as claimed in claim 1 in which SiO₂+Al₂O₃>98%.
 9. A needled blanket as claimed in claim 1 having a shot content of less than 45 wt % or less than 44 wt % or less than 43 wt %.
 10. A needled blanket as claimed in claim 1, in which the needled blanket has a tensile strength to density ratio of >0.39 kPa/kg·m⁻³ or >0.43 kPa/kg·m⁻³ or >0.45 kPa/kg·m³.
 11. A needled blanket as claimed in claim 1, in which the specific surface area is in excess of 0.3 m²·g.
 12. A needled blanket as claimed in claim 1, in which the inorganic fibres have an arithmetic mean diameter <2.5 μm.
 13. A needled blanket as claimed in claim 1, in which the inorganic fibres have an arithmetic mean diameter <2.25 μm.
 14. A mass of melt-formed inorganic fibres having a shot content, of shot >45 μm, of less than 51 wt %, a specific surface area (BET)>0.25 m²·g⁻¹. and suitable for needling to form a blanket as claimed in claim
 1. 15. A self-supporting insulating body other than a needled blanket, formed of fibres as claimed in claim 14 and having a shot content, of shot >45 μm, of less than 51 wt %, a specific surface area (BET)>0.25 m²·g⁻¹.
 16. A self-supporting insulating body as claimed in claim 15, in the form of a monolithic refractory fibre module having a shot content, of shot >45 μm, of less than 51 wt %, a specific surface area (BET)>0.25m²·g⁻¹.
 17. A needled blanket comprising melt-formed inorganic fibres having an overall composition in weight percent SiO₂: 47 to 65% Al₂O₃: 35 to 53% the needled blanket having a shot content, of shot >45 μm, of less than 51 wt %, and a specific surface area (BET)>0.25 m²·g⁻¹, wherein SiO₂+Al₂O₃>98%. 